One of most important things of a next generation wireless access system is to satisfy data transfer rate demand. To this end, ongoing effort to develop various technologies including MIMO (multiple input multiple output), CoMP (cooperative multiple point transmission), a relay and the like is in progress.
In a wireless access system according to a related art, even if an uplink (UL) and a downlink (DL) are set to differ from each other in bandwidth, a single carrier is mainly taken into consideration. For instance, a wireless communication system having UL and DL carriers, each of which number is 1, and UL and DL bandwidths generally symmetric to each other is provided based on a single carrier.
Yet, considering the situation that frequency resources are saturated, as a method of securing broadband bandwidths to meet the higher data transmission rate requirements, CA (carrier aggregation/multiple cells) is introduced in a manner of designing each of scattered bandwidths to operate an independent system and aggregating a plurality of bands into a single system.
In this case, a carrier of an independently operable bandwidth unit is called a component carrier (hereinafter abbreviated CC). In order to support an increasing transmission size, 3GPP LTE-A or 802.16m keeps extending its bandwidth up to 20 MHz or higher. In this case, at least one or more component carriers are aggregated to support the broadband. For instance, if a single component carrier supports a bandwidth of 5 MHz, 10 MHz or 20 MHz, a system bandwidth is supported up to maximum 100 MHz by aggregating maximum 5 component carriers together.